Roller Compacted Concrete Buttress at the Site C Clean Energy Project

The project is a 1100 MW generating station on the Peace River near Fort St. John, BC, Canada.
The project is underlain by dark grey moderately weak, flaky to fissile, silty shale, interbedded
with thin beds of siltstone, sandstone and shale. Thick glacial deposits were eroded as the ice
masses receded and the Peace River down-cut a valley resulting in substantial redistribution of
stresses in the river valley walls and an upward bulging of the valley floor and inward relaxation
of the valley walls. Shear movement along thin weak bedding planes and local thrust faults
also developed. Near-vertical jointing, parallel to the valley walls, weak bedding planes and
cross-cutting discontinuities have been identified in both abutments. The original configuration
of the spillway headworks and intakes were concrete gravity structures founded on deep cuts in
the bedrock with weak bedding planes that daylight in the excavated slopes. A new layout was
developed where the horizontal water forces on the headworks structures were taken down an
inclined “buttress” to the bedrock below the river valley floor and by-passing the weak bedding
planes located in the valley walls. This resulted in the unique concept of the RCC Buttress supporting
the headworks structures, powerhouse and spillway structures.

Heidstra, N., J. Nunn, A. Watson, K. Dodman, R. Carter, and L. Burmeister. 2017. “Roller Compacted Concrete Buttress at the Site C Lean Energy Project.” Canadian Dam Association Bulletin. 28(3): 12 -23.